Centrifugal-type vapor source



July 4, 1967 H, R, SMH-H, 1R 3,329,524

CENTRIFUGL'TYPE VAPOR SOURCE Filed June 12, 1963 5 Sheets-Sheet l hina 23305) July 4, 1967 H. R. SMITH, JR

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CENTRIFUGAL- TYPE VAPOR SOURCE Filed June 12, 1963 5 Smets-Sheet 3 United States Patent O 3,329,524- CENTRlFUGAL-TYPE VAPGR SUURCE Hugh R. Smith, Jr., Piedmont, Calif., assigner to Temescal Metallurgical Corporation, Berkeley, Calif., a corporation of California Filed .lune 12, 1963, Ser. No. 287,386 17 Claims. (Cl. 117-107) This invention relates to an improved method and apparatus for producing vapors in a vacuum with a focused Vapor source, particularly a centrifugal-type vapor source wherein the vapors are produced from a ring of molten matter held flat against the inside of a rotating cylinder by so-called centrifugal force.

Prior art vapor sources are usually planar, without vapor focusing means, and produce a vapor cloud which rises vertically. Consequently vapor deposition must be achieved upon the underside of a horizontally disposed substrate, and vertically disposed substrates cannot be readily coated. Another deficiency of a conventional planar source is that vapor clouds diffuse, decreasing the original vapor density. High Vapor `density is conventionally attained by increasing the heat supply to vaporization sources or by using a plurality of overlapping vapor sources, -but both techniques result in increased operational expense. Superheating of the vapors, which produces certain enhanced coating characteristics, must also rbe achieved 'by the use of additional apparatus, again increasing expense. In order to provide an alloy coating to a substrate, a plurality of planar sources are often simultaneously employed, thereby attaining a vapor cloud with a plurality of Vapor elements. However, the use of a plurality of sources wastes valuable space within the vacuum chamber, and it would be desirable to accomplish superheating and alloy deposition of coatings in some other manner, preferably with one compact piece of apparatus.

It is an object of the present invention to provide a vapor source capable of coating vertical substrates.

It is another object to increase the thermal efiiciency of a vapor source of providing method and means for increasing vapor density and for focusing and superheating the vapor cloud.

It is a further object of this invention to provide an improved vapor source providing for rapid changes between materials vaporized.

It is still another object of this invention to provide an improved vapor source producing a homogeneous vapor mixture for alloy coatings from a single source.

In accordance with this invention, a hollow cylinder containing material to be evaporated is rotated about its central axis within a vacuum chamber and heated to form a rotating, molten ring of evaporating material. This ring is maintained in a molten state by directing one or more heat sources on the surface thereof. The molten material assumes the circular shape of the inside of the cylinder, and is held there by centrifugal force. The material is evaporated from the molten ring to produce vapors. The vapor particles move from the liquid and build up pressure in the cylinder. A reflector is placed inside and against a closed end of the cylinder. Vapor particles striking the reflector are forthwith reemitted from the hot surface thereof. The vapor particles leave the respective surfaces in all directions, lbut for geometrical reasons the most likely direction is normal and near normal to the surface. One end of the cylinder is open to the evacuated chamber. The vapor particles move in all directions, striking one another and the various surfaces inside the cylinder. However, because of the end open to a vacuum, the average velocity of the vapor is in the direction of the open end. The masking effect of the cylinder walls and the shape of the reflector produce ice a more or less focused beam of vapor moving axially out of the open end of the cylinder. As used herein, beam of Vapor and directed beam of vapor mean a stream of vapor particles moving generally in the same direction or nearly the same direction and include a diverging stream. The axis of the beam may be horizontally disposed. Thus, a substrate which is vertically disposed may be readily coated by employing a cylinder which is rotated about a horizontal axis, and which emits horizontally directed vapors. For example, long, thin sheets of material can be placed vertically and coated; particulate substrates dropped across the open end of the cylinder can be coated; and by using two opposed cylinders, both sides of a substrate can 'be coated at the same time. This latter capability has heretofore been considered extremely impractical with vertically rising vapors from conventional vapor sources. The material being evaporated can be replenished by injecting solid material into the heated, mol-ten ring, and, in this manner, continuous operation is provided.

Evaporation may be achieved with a single evaporating material within the rotating cylinder, or it may be achieved by providing a rotating pool of material with a high boiling point and low evaporation rate within the cylinder, and injecting a second material with a lower boiling point and a relatively high evaporation rate into the molten pool so formed. The pool may be heated above this lower boiling point. Under such conditions, the injected material is almost immediately vaporized to produce the desired vapor cloud, with the molten pool providing the necessary heat and acting as a secondary heat source.

- Thus, substantially instant evaporation occurs, and, in the event it is desired to change from one substance to another, the change can be easily accomplished by merely injecting a new substance into the molten secondary heat source. Rapid changeover from the first vaporized substance to the second vapor-ized substance is lthus quickly and economically accomplished, providing a highly flexible evaporation source.

Homogeneous mixtures of vapor providing alloy coatings may -be obtained by first melting a metal of higher boiling point, which will serve las a secondary heat source in the spinning cylinder, as above. This metal may be held in place by centrifugal force, While a plurality of other metals, of much lower :boiling points and relatively high evaporation rates, are injected simultaneously into the secondary heat source to evaporate almost instantly and provide la homogeneous vapormixture. The proportionate amount of each constituent vapor element may be easily regulated by varying the feed rate of the injected substances. Thus, a highly fiexible method of applying alloy coatings is also provided herein.

Other objects and advantages of the invention will become apparent from the following description and the accompanying drawings, illustrating preferred embodiments of this invention.

FIGURE 1 its an end View of a crucible and other apparatus, partially in section, embodying this invention and adapted to carry out the new method disclosed herein;

FIGURE 2 is a sectional view of a rotating vapor source taken in the plane 2-2 of FIGURE 1;

FIGURE 3 is a transverse sectional view of an alternative embodiment of the reflector illustrated in FIGURE 2;

FIGURE 4 is an enlarged view of an alternative form 0f the inwardly facing groove shown in the inside periphery of the cylinder lining shown in FIGURE 2;

FIGURE 5 is an enlarged sectional view of an alternative embodiment of the source groove of FIGURE 4;

FIGURE 6 is a diagrammatic view of the present invention showing the simultaneous coating of both sides of a vertically disposed substrate;

FIGURE 7 is a side view, partly in section, showing a modified form of the apparatus shown in FIGURE 2, including means for changing the direction of the vapor;

FIGURE 8 is a sectional View of a modified form of the vapor source, wherein the crucible is rotated about a vertical axis', and

FIGURE 9 is a sectional View of a focused vapor source that is an alternative to the source illustrated in FIGURE 2.

By thi-s invention there is provided an improved method of coating substrates by vapor deposition, in accordance with the steps set forth below. ln a preferred form of this invention, a rotating ring of molten material is formed by heating and melting the material within a spinning container, the material being held against the interior of the container by centrifugal force. The rotating ring may be rotated .about an axis at any desired angle and the vapors evaporating from the interior surface of the rotating, liquid ring directed out of the open end of the container, generally axially of the rotating ring. Additional material for evaporation is added by injecting it directly into the hot, liquid ring, as, for example, through .a vaccum lock provided in the wall of the vacuum chamber. Suitable heating is supplied to melt and vaporize the material, as further described below.

The injection rate is chosen so that the evaporation rate of the material is equal lto its injection rate, thereby providing a continuous vapor generation. The molten ring acts as a secondary heat source providing the heat necessary to melt the newly injected material, and the ring itself is heated by other heating means acting as a primary heat source. As mentioned above, the vapors are evaporated from the interior surface of the rotating, liquid ring. These vapors will then issue from the open end of the ring and by rotating the ring about a horizontal axis, the vapors are made to issue generally horizontally. These vapors may then be directed yagainst a vertically disposed substrate placed across the path of the horizontally travelling vapors, Where they deposit to form a coating.

Vapor deposition may also be easily achieved employing two different materials with different evaporation rates. To accomplish this, the rotating ring may be formed of a metal having a high boiling point, such as a refrac' tory metal, for example, zirconium, columbium, tantalurn. hafnium, uranium, tungsten or molybdenum. Compounds of certain metals may lbe also used, for example, the nitrides of aluminum and boron, or the borides of hafnium, zirconium, titanium and tantalum. These metals or compounds have a very high boiling point and a very low evaporation rate at high temperatures. Thus, once they are "formed into a rotating ring they are admirably suited for use as a secondary heat source for vaporizing injected materials without emitting any substantial amount of their own vapors. The injected material, for example, aluminum, with a lower boiling point and ya relatively high evaporation rate, is injected into the molten lrotating ring. Rapid evaporation results and the vapors of the injected aluminum are emitted for deposition upon a substrate placed in front of the open end of the rotating container and across the path of the directed vapors, as above-described. Since the evaporation rate from the materi-al of the secondary heat source is small, only a negligible amount of it will evaporate, and a substantially pure vapor of the injected material will be produced. Also, when a material with a very high boiling point (for example, a refractory metal) is used for the secondary heat source, superheating of the injected aluminum, or the like, will be greater because the aluminum will evaporate and be subjected to temperatures well above its boiling temperature by radiation from the surrounding rotating ring, Which is `at a relatively high temperature.

Referring now to FIGURES l and 2, showing a preferred embodiment of this invention, it will be seen that within a vacuum chamber 11 defined by casing 12 `and evacuated by a vacuum pump 10, there is disposed a rotating crucible 13. The crucible is preferrably formed as a Water-cooled, copper cylinder with cooling passages 14, and is provided with end heat-resisting bafes 15, and an insulating refractory liner 16. A reflector 17 closes one end of the crucible, as shown. The liner, baffles and reflector are preferably made of carbon, or some other material suitable for high temperature insulation of the metal walls of the crucible 13. For example, a cylinder of carbon may be machined with a six-inch inside diameter and an eight and onequarter inch outside diameter to serve as a liner 15, and to fit into a water-cooled copper crucible 13 of an eight and one-quarter inch, inside diameter. When evaporating high boiling point materials or highly reactive materials, cylinder 13 and liner 16 must be constructed of material capable of accommodating the temperatures and materials involved. Thus, while it is not necessary to provide cooling apparatus for low temperature operation, high temperature evaporation may require that the crucible be cooled.

The insulating refiector 17 may be fitted into the liner 16 Within crucible 13. It serves as a focusing device for focusing the vapor generated Within the crucible 13. The reflector 17 may be constructed so that its surface reemits or reflects the vapor particles preferentially in the desired direction parallel to the axis of the crucible and toward the open end of the crucible, as indicated by the arrows appearing in FIGURE 2. By appropriate shaping of the reflector, the stream of vapor may be made more concentrated or more divergent. Crucible 13 is rotated by a variable speed motor 1S, which may be disposed within vacuum chamber 11 or placed outside of the chamber and connected to the crucible 13 through a shaft 19 extending through a conventional vacuum seal Ztl.

In operating the apparatus described above, the crucible 13 is rotated about a horizontal axis until the desired rotational speed is attained, for example 250 to 450 r.p.rn. A material 21 is fed into the crucible at an annula-r groove 22 formed about the inner surface of the liner 16. This groove serves as a retainer for the molten material, and in actual practice may be made very narrow and shallow; for example, the groove may be 3" wide and l deep.

Continuous feeding of material to be evaporated is provided by feeding a wire or the like of material 21 into the vacuum chamber 11 through a conventional vacuum lock 23. The material 21 is melted within the crucible by ian electron beam 24, which is generaated by electron beam generator 25. The electron beam 24 is focused into the path shown by a transverse magnetic field directed at right angles to the plane of FIGURE 2. As the material 21 is fed into the beam 24.in the crucible, the material melts in the groove 22, forming a molten pool of material 26 in the form of a ring as the crucible is rotated. During vaporization, the feed material Z1 is injected directly into the molten ring 26 because continuous direct melting in the electron beam 24- might produce excessive sputtering and splattering, which is undesirable during the vapor deposition process. The electron beam 24 supplies the energy to melt the feed wire 21, maintain the molten pool 26, and vaporize the liquid material within said pool.

It is important that the heat for vaporization be applied to the surface of the liquid in order to prevent bubbling. The operation of electron beam sources and their focusing and control by magnetic fields is well-known to those skilled in the art, and thus no detailed description thereof is included herein. The electrons may be emitted from an electron source such as `a heated filament. These electrons may then be accelerated by an appropriate electrical field into a beam which may be bent, as shown, by an appropriate magnetic field. This magnetic field is preferably transverse to the electron beam rather than coaxial therewith, for axial magnetic focusing would cause positive ions to be axailly focused back into the electron beam gun. The transverse mangetic field does not bend the trajectory of the positive ions to the same extent as that of the electron beam, so with a transverse magnetic field the positive ions are not focused 'at the electron beam gun. The vapor produced may develop pressures in the crucible 13 of the order of l mm. Hg, preferably from 0.1 to l0 mm. Hg. At such pressures many of the electrons in the beam do not reach the molten ring 26 directly but are scattered. The scattered electrons have lower energy than those in the original beam and are influenced by the magnetic field to move sideways in spiral paths to strike the surface of the molten ring on the side rather than on the bottom. Thus these scattered electrons are not lost and substantially all of the energy of the original electrons is dissipated within the crucible 13, -most of it reaching the surface of the molten ring, and `goes to vaporize the molten material and superheat the vapor. The pressures developed in the crucible are high `relative to the pressure in the vacuum chamber 11; thus, the vapors in the crucible are in a superheated state when they reach the chamber 11 at the lower pressure. Superheated vapor makes for more uniform deposition of the material on the substrate 27, positioned before the open end of the crucible 13.

The electron beam generator may be disposed so that the beam is bent more than 180. By bending the beam as much as 270, the generator can be disposed more out of the way of the beam. It is desirable Ato shield the generator from the vapor so that the vapor does not befoul the generator. n

It should be noted that feed material 21 is not limited to wire form. Other forms of feeding the material may be employed, as, for example, moving a solid rod, dropping in small pieces, or feeding molten material or air-driven powder into the molten ring 26. However, for simplicity, the feeding system is herein referred to as a feed wire.

It is known in the prior art to employ a rotating vapor source to coat substrates by vapor deposition. This vapor deposition of the prior art is effected by passing the substrate through the vapor source and along the axis of rotation thereof. Vapors reach the substrate radially from all directions. Such a source has numerous disadvantages, some of which may be briefly stated. Wide sheets of material cannot be coated, since a container of large diameter would be required. Coatings may be desired on one side of a substrate, and the conventional rotating vapor source must coat all sides of a substrate passed through it. The substrate itself, being passed through the axis of the rotating, liquid metal, will become heated, and this heat will inhibit vapor deposition. Thus, the preferred method of this invention contemplates deposition on a substrate placed outside of the rotating container, by vapors traveling out of the source axially of the hot, molten ring in order to attain certain advantages of this invention. The present invention is advantageous over the prior art in separating the surface to be coated from the high temperature region, for it is possible to achieve more efficient condensation of the vapors on a cold substrate.

The method of the present invention also provides for the utilization of one molten material as a secondary heat source to heat other material to be vaporized. In the apparatus of FIGURES 1 and 2, a metal having a relatively high boiling point at the prevailing pressures, for example zirconium, is rst melted in the inward-facing groove 22, until the inward-facing groove is partially filled with a molten rotating ring of zirconium.

The material to be evaporated, having a lower boiling point and a relatively high evaporation rate at such pressures, for example aluminum, is then injected directly into the molten zirconium ring. The aluminum will evaporate rapidly because the temperature of the zirconium pool 26 is maintained by the electron beam 24 above the boiling temperature of the aluminum. The aluminum feed wire is preferably inserted away from the point where the electron beam 24 strikes the molten ring of zirconium and not directly intothe electron beam 24. This reduces the spray and splatter occasioned by the degassing of the metal as it melts. If the feed rate ofthe aluminum feed wire 21 is properly selected, which may be on the order of 50 per minute, the aluminum Will vaporize almost instantaneously. At the preferred temperature, zirconium is still sufficiently below its own boiling point `so that its evaporation rate is negligible, providing a substantially pure aluminum vapor.

The aluminum will partially dissolve in the zirconium, but most of it will float on top. It has been observed that under operating conditions, bands of molten metal are formed, with zirconium isolating the aluminum from the liner 16. The zirconium is less active than the aluminum and keeps the aluminum from attacking the liner. Further, the zirconium is a relatively poor heat conductor and thus partially insulates the liner 16 and the crucible 13 from the electron beam 24, keeping the crucible cool while at the same time keeping the aluminum hot.

A quick change from one vaporizing material, such as aluminum, to another material, such as silver, is achieved merely by :removing the aluminum feed wire 21 and inserting another feed wire made of silver. By doing this, the source of aluminum vapor is immediately exhausted, and a new source is at the same time provided. The zirconium pool 26 and crucible 13 remain in rotational motion, and no time is lost in stopping and re-starting the process. In addition, since the zirconium pool 26 remains within crucible 13, there is no need to reheat either the crucible 13 or the pool 26, and efficiency is thereby maximized.

Furthermore, a plurality of wires, made of relatively low boiling point metals, may be simultaneously employed to provide a homogeneous vapor mixture to form an alloy coating on the substrate 27. For example, if an aluminum and silver coating is desired on substrate 27, a second feed material 21 (indicated by dashed lines in FIGURE 2) may be inserted, at an injection rate which will give the desired percentage composition. The vapors of both elements will be mixed in crucible 13 by thermal diffusion and the rotation of the crucible. Alternatively, the single rod may be made of the desired alloy.

An important feature of this invention is the focusing of the vapor particles to form a directed beam or cloud moving axially of the crucible 13. With one end of the crucible closed, pressure builds up in the crucible and ejects the vapor into the evacuated chamber 11. The shape of the crucible causes the vapor to be emitted in a directed, symmetrical, more or less concentrated beam. Although most of the vapor particles are initially emitted more radially inward, their interactions with each other and with the reector produce a more -axial motion so that the particles leaving the open end of the crucible are mostly moving principally axially. Further the radial components concentrate the beam along the axis, much as water from a nozzle. The extent of the divergence of the beam is influenced by the shape of the reflector. It is often important to produce a divergent beam so that the substrate may be uniformly coated over a wide area, yet not so diffuse as to make it undirected and deposit a lot a material on other than the substrate. In FIGURE 3 is shown a reflector 17 of a shape effective to produce a more divergent yet directed beam. The protruding more or less conical section 17 reduces the density of the center of the beam and disperses the vapor more widely.

In FIGURE 4 is illustrated an alternative form of the invention wherein vapors of two materials are produced simultaneously. Rather than using a refractory material as a heat source, a base material is used that will evaporate at the operating temperatures and a second material boiling at a lower temperature is added. The operating temperature may even be so high as to vaporize a refractory material. For example, to make a coating of an alloy of columbium and tin, a columbium rod 36 is melted to form a ring 38 in the groove 22 at a rate to provide the desired amount of columbium vapor, and a tin rod 35 is melted into the ring 38 at a rate to provide the desired tin vapor. The liquid tin dissolves somewhat in the columbium but most oats thereon as ring 37, leaving exposed surface rings of Columbium. In either case, both the tin and the columbium liquids have surfaces whence vapor particles thereof are emitted. The relative amounts of each that are vaporized is controlled principally by the rate of feed of the tin rod, for the tin vaporizes substantially as soon as it is inserted, whereas the columbium is vaporized by the energy left over after the vaporization of the tin.

Referring to FIGURE 5, it will be seen that a mixed vapor cloud may be provided by employing a divided groove 40, having at least one annular dividing partition 41. This partition is provided with 4channels 42 axially of the Crucible, so that the material 43 with the higher melting point and density extends into both portions of the groove by iiowing through channels 12. A material 44 having a relatively low density, injected only on one side by feed wire 45, will not ow to the left side of partition 41, since in this example it is lighter and will float on top of material 43 so that it cannot reach the Channels 42. Replenishment of material 43 is accomplished by using a second feed Wire 46. Where the lighter material dissolves to an appreciable lextent in the heavier, some of the lighter material will pass through the channels 42. However, generally speaking, the partition 41 is effective to preserve separate surfaces of the respective materials, whereby both materials can be vaporized at once. By supplying vapor from each side of the partitioned groove, the vapor cloud will comprise a mixture of the two materials and will provide an eicient means of applying an alloy coating to a substrate.

Referring to FIGURE 6, it can be seen that this invention, when operated in horizontal position, may be employed to coat vertically disposed substrates. For example, thin sheets of glass which can be vertically draped, but which will not withstand horizontal suspension without cracking, may be readily coated. Also the invention is applicable to coating both sides of a long, thin, continuous roll of sheet material, and FIGURE 6 illustrates one source arrangement for this purpose. Since there is, or can be, a large number of duplicate elements, the duplicate elements will be designated by the same numerals, followed by the symbol prime The variable motors 60, 66 are connected to crucibles 61, 61 through shafts 62, 62 which extend through conventional vacuum seals 63, 63. A large roll 641 is rotatably mounted by any suitable means 65 to supply a continuous thin sheet of material 66. This sheet 66 is directed between a pair of vapor sources, as described above, through a conventional vacuum seal 67 and about rollers 68 and 69. The sheet further passes through another vacuum seal 7 t1 and about a roller 71 onto a driven receiving roller 72. Sheet 66 is thusly vertically disposed between rotating crucibles 61 and 61 to receive vapor deposition on both sides in one, time-saving, efficient pass through the vacuum chamber 73, defined by structure 74, and evacuated by a conventional vacuum pump 75. The sheet 66 may simultaneously be coated with two layers, having different chemical compositions by employing different chemical substances in the crucibles 61 and 61. Again this is accomplished in one efficient pass of sheet 66 through the vacuum chamber 73.

It should be noted that while the invention has been described above for a horizontal disposition of the crucible 13, the invention is not limited to such disposition alone. The cylinder may be mounted at any desired angle. As shown in FIGURE 7, means may be provided for changing the angle of disposition. As shown in FIGURE 7, the vacuum seal 26 may be pivotal so that the shaft 19 can not only be rotated about its axis but its axis may be pivoted. As shown, the motor 1S is adjustably mounted on a truck 76 running on wheels 77 which permit lateral pivoting of the truck 76, motor 1S and shaft 19. Pivoting in the vertical direction may be achieved by adjusting the mounting as by hydraulic pistons 7d. The electron beam generator 25 and a wire feeding mechanism 79 may be attached to a bracket 30 mounted to pivot with the axis of the shaft 19 so as to maintain the positions of the generator 25 and mechanism 79 relative to the Crucible 13.

Although the major advantages of the invention accrue for other than the vertical disposition of the Crucible, there are uses for which vertical disposition is satisfactory or even preferred. In Cases where the Crucible may rotate about an axis near vertical, the invention may take the form illustrated in FIGURE 8. In this form of the invention, there is no reflector 17. The liner 16 extends over the entire interior surface of the Crucible 13, and the crucible is rotated at such speed that some, but not all, of the molten metal is held by centrifugal force against the side wall of the liner 16. The rotation is slow enough that some of the molten metal remains on the bottom, so that the metal forms a cup-shaped surface, the depression of which is determined by the rate of rotation. By making the surface relatively depressed, the Vapor emitting surface is made much like that of the apparatus of FIGURES 1 and 2 but provides a larger surface permitting faster evaporation. Further the inside bottom surface of the liquid metal serves substantially the same focusing purpose as the reflector 17 of FIGURES l and 2, and the resultant vapor beam is substantially the same as with the apparatus of FIGURES 1 and 2 except vertical instead of horizontal.

Although in the preferred forms of the invention, as described above, the vapor source was of the centrifugal type, it is also within the scope of the present invention to achieve a focused beam that may extend horizontally without a rotating crucible by using appropriate reectors. The rotating Crucible provides a larger surface area of the liquid and more uniform heating `over a larger area of the liquid which permits more vaporization without bubbling and a symmetrical beam; however, for certain applications, it is practical to achieve the results by focusing. Such an arrangement may be as shown in FIGURE 9. The apparatus may be as shown in FIGURE 2 except that the Crucible is not rotated :but is rigidly mounted on brackets 81, and the pool 82 of liquid is not in the shape of a ring, the liner 16 being formed in the shape of the ring of FIGURE 2. With such an arrangement many of the vapor particles from the pool strike the surface 83 of the liner 16, which like reflector 17 reemits the particles, principally radially. Some heat is conducted away from the liner 16, and therefore some vapor may condense on its surface 83, but the condensed liquid will then run back down into the pool 82. The net effect is like that produced by the apparatus shown in FIGURE 2, for the surface of liner 16 emits vapor particles in the same directions as the surface of the ring 26 that it replaces. The surface 83 is heated by the latent heat 'of vaporization of the condensing vapors, by radiation and by electron bombardment. Similarly other heat shields placed outside the opening of the Crucible can be used for reectively directing the vapor stream, these shields being similarly heated.

Thus, this invention, in its broader aspects, is not limited to the speciiic examples herein illustrated and described, and the following claims are intended to cover all changes and modifications that do not depart from the true spirit and scope of this invention.

What is claimed is:

1. An improved method of vacuum coating a substrate by vapor deposition Comprising the steps of:

(a) forming a ring lof molten material within a rotating container having an open end axially thereof by spinning the Container to hold molten material against the interior thereof by centrifugal force;

(b) evacuating the space external of the open end;

(c) heating the -ring of molten material to vaporize the material;

(d) injecting yadditional material to be evaporated into the molten ring of material; and

(e) positioning a substrate in said `space in front of said open end for receiving vapor deposition from vapor issuing axially out of said open end.

2. An improved method of coating a substrate in vacuum by vapor deposition comprising the steps of:

(ya) forming a ring of a molten first material within a rotating crucible having an open end axially thereof by yspinning the Curcible to hold molten material against the interior thereof by centrifugal force;

(b) applying heat to the surface of said first material to heat it t-o `a temperature below the boiling point of said first material and above the boiling point of a second material;

(c) feeding said second material onto the rotating ring of molten first material; and

(d) positioning a substrate outside of and in front of the open end of the crucible for vapor deposition thereon by vapor issuing from the 'open end of the crucible.

3. An improved method of coating a substrate in Vacuum by vapor deposition comprising the steps of:

(a) forming a ring of a molten first material within a rotating crucible having an 'open end `axially thereof by spinning the crucible to hold molten material against the interior thereof by centrifugal force;

(b) applying heat to the surface of `said first material to heat it to a temperature at which said first material vaporizes;

(c) feeding said first material and a second material onto the rotating ring of molten first material, said second material vaporizing more readily than said first material at said tempe-rature; and

(d) positioning a substrate outside of and in front of the open end of the Crucible for vapor deposition thereon by vapors of both of said first and second materials issuing from the open end of the crucible.

4. An improved method 'of coating -a substrate in vacuum by vapor deposition comprising the steps of:

(a) forming a ring of a molten first material within a rotating crucible having an open end axially thereof by spinning the crucible to hold molten material against the interior thereof by centrifugal force;

(b) applying heat to the material to heat it to a ternperature below its boiling point;

(c) feeding at least two other materials onto the rotating ring of molten first material, said other materials vaporizing at said temperature; and

(d) positioning a substrate outside of and in front of the open end of the crucible for vapor deposition thereon by vapors of said other materials issuing from the open end of the Crucible.

5. A method of vacuum Coating a substrate by vapor deposition comprising the steps of: rotating a crucible having an open end axially thereof and containing molten material held against the interior thereof by centrifugal force, evacuating the space external of the open end, heating the molten material to vaporize material from the surface thereof, and positioning a substrate in said space in front of said open end for receiving deposition of vapor issuing axially yout of said open end.

6. The method according to claim wherein the vapor is focused into a directed stream with hot surfaces, said stream being directed axially out of said open end.

7. The method according to claim 5 wherein said crucible is rotated about an axis disposed at a substantial angle from the vertical and the rotation of said crucible holds molten material in a ring against the interior of said crucible.

8. The method according to claim 5 wherein the rotation of the crucible is about a substantially vertical axis with the open end up at a rate sufficient to depress the center of the surface of the molten material substantially so that the vapor travels in a focused beam generally axially from the open end of the crucible.

9. The method according to claim 5 wherein the direction of the axis of rotation is changed while the crucible is rotating, thereby changing the direction of the vapor stream.

10. The method according to claim 5 wherein said molten material is heated by directing an electron beam through said open end upon the surface thereof to form vapors initially travelling generally normal to the surface of the rotating molten material toward the axis of rotation, and said vapors are thereafter focused into a stream directed axially out of said open end.

11. A method of vacuum coating -a substrate by vapor deposition comprising the steps of: rotating a crucible having an open end axially thereof and containing molten material held in a ring against the interior thereof by centrifugal flor-ce, said crucible being rotated about an axis disposed at a substantial angle from the vertical, evacuating the space external of the open end, heating said material by directing an electron beam through said open end upon the surface of said rotating ring of molten material to vaporize material from the surface thereof, and positioning a substrate in said space in front of said open end for receiving deposition of vapor issuing axially out of said open end.

12. A centrifugal vapor source for Coating substrates comprising an enclosure defining a vacuum chamber, means for evacuating said vacuum chamber, a cylindrical crucible disposed within said vacuum chamber and having one end axial and vopen to said chamber, a shaft secured to said crucuible axially thereof at the end remote from said one end, means for mounting said shaft through said enclosure for rotation about its axis, means externally of said enclosure for rotating said shaft and the crucible secured thereto at a rate sufficient to hold material within said crucible against the interior walls thereof by centrifugal force, said crucible being provided with passages for the circulation of cooling fluid, means for circulating cooling fluid within said passages, an electron beam generator within said vacuum chamber for directing a beam of electrons through said open end to evaporate material within said crucible disposed against said interior walls, said electron beam generator being mounted in a position spaced from said open end and so that the walls of said crucible shield said electron beam generator from the vapors issuing from said open end, and means for posi-` tioning a substrate in front of said open end of said crucible for the deposition of vapors upon said substrate.

13. Apparatus according to claim 12 including means defining a reflecting surface at the end of said crucible opposite said open end and shaped to focus the vapor particles into a directed stream axially from said open end.

14. Apparatus according to claim 13 wherein said means dening said reflecting surface at said closed end defines a reflecting surface extending Centrally thereof toward `said open end so as to direct vapor particles from said open end in a divergent directed stream.

15. Apparatus according to claim 12 wherein said axis is at a substantial angle from the vertical.

16. Apparatus according to claim 12 wherein said means for rotating is yoperable to rotate said crucible at a velocity sufficient to hold molten material therein as a ring against the walls of said crucible whereby vapor issues from said container in a direction generally parallel to the axis of rotation.

17. Apparatus according to claim 12 including means for changing the direction of said axis to change the direction of said vapor stream.

(References on following page) 11 i2 References Cited 3,029,777 4/1962 lCeryck et a1. 118-49 UNITED STATES PATENTS 3,046,936 7/ 1962 Simons 11S-49.1

1/1954 Clough et a1. 11s-49 X FOREIGN PATENTS 5/1956 Steigerwzdd 118-49 X 5 882,171 7/1953 Germany,

4/1960 Frank 11S-49.1 X 140,259 5/1953 Sweden.

8/1961 Smith 118-49 X I 1/1962 Valsh 117 1071 X ALFRED L. LEAVITT, Prlmmy Exammel.

2/1962 Alexander 118 49 X 10 IVURRY KATZ, Exflmlner.

3/ 1962 Theodoseau et al. 118-49 X A. GOLIAN, Assistant Examiner. l 

1. AN IMPROVED METHOD OF VACUUM COATING A SUBSTRATE BY VAPOR DEPOSITION COMPRISING THE STEPS OF: (A) FORMING A RING OF MOLTEN MATERIAL WITHIN A ROTATING CONTAINER HAVING AN OPEN END AXIALLY THEREOF BY SPINNING THE CONTAINER TO HOLD MOLTEN MATERIAL AGAINST THE INTERIOR THEREOF BY CENTRIFUGAL FORCE; (B) EVACUATING THE SPACE EXTERNAL OF THE OPEN END; (C) HEATING THE RING OF MOLTEN MATERIAL TO VAPORIZE THE MATERIAL; (D) INJECTING ADDITIONAL MATERIAL TO BE EVAPORATED INTO THE MOLTEN RING OF MATERIAL; AND (E) POSITIONING A SUBSTRATE IN SAID SPACE IN FRONT OF SAID OPEN END FOR RECEIVING VAPOR DEPOSITION FROM VAPOR ISSUING AXIALLY OUT OF SAID OPEN END. 